The invention relates to fiber optic systems. Particularly, the invention provides a method and apparatus for coupling high intensity light into a low melting point optical fiber using a homogenizer to provide a more uniform intensity distribution.
In the field of fiber optic illumination systems, it is known that optical power output from arc lamps, such as xenon lamps and metal halide lamps, can reach hundreds of watts. The fiber optic that transmits light from these light sources to the applications consists of single fibers or fiber bundles which can be made out of quartz, glass, or plastic. Plastic fibers intrinsically cannot operate at high temperature. While single glass and quartz fibers can operate at relatively higher temperatures, fiber bundles containing such fibers are still temperature sensitive due to the epoxy in between the individual fibers.
Light emitted from the arc lamp is usually coupled to a fiber optic by the use of mirrors and lenses either alone or in combination. To preserve the brightness of the arc as much as possible, an optimized optical system will produce an image of the arc on the fiber optic with as small a spot as possible and constant magnification. Due to the intrinsic nature of the arc itself, the intensity is non-uniform, as a result, the image of the arc at the fiber optic will also be non-uniform, thus producing xe2x80x9chot spots.xe2x80x9d These hot spots may produce intensities higher than the material damage threshold of a particular fiber optic at a localized spot before the average intensity across the fiber reaches such value. This causes substantial damage to the fiber optic. Therefore, the total power which can be delivered through the fiber optic for a non-uniform image is necessarily less than that for a uniform image. Thus, it is desirable to have an input intensity profile as uniform as possible such that the overall power can be increased before the damage threshold is reached at any single point. This will allow more light to be coupled into the fiber optic without damage.
Several methods have been used to couple more power into low melting point fibers. U.S. Pat. No. 5,898,802, the specification of which is herein incorporated by reference, discloses a method of using fused bundles to spread the intensity profile of light beam, thus reducing the peak intensity and allowing more light to be coupled into the polymer fiber. Although the use of the fused bundle spreads the intensity profile, it has a limit and does not totally produce a flat profile. U.S. Pat. No. 5,761,356 discloses the use of a spatial filter to filter out any unguided mode in the input beam to the output of a low melting point fiber. While this approach reduces the dissipation of heat from unguided modes at the input end of the fiber, the profile of the light is still non-uniform, and thus does not produce optimum results.
It is therefore an object of the present invention to provide a method and apparatus for providing a uniform intensity profile light beam to an optical fiber.
Further, it is an object of the present invention to provide a method and apparatus for providing efficiently coupling high intensity light into low melting point optical fibers.
The present invention provides a method and apparatus for coupling high intensity light into a low melting point optical fiber using a homogenizer which is a section of an optical waveguide with a polygonal cross-section. The homogenizer allows a low melting point fiber to be positioned away from the focus of the coupling system, and simultaneously provides a mixing mechanism in which the non-uniform intensity profile of the input light will become substantially uniform at the output. This allows more light to be coupled into the fiber optic before any portion of the fiber reaches the damage threshold. Preferably, the homogenizer is a section of an optical waveguide having at least a partial polygonal cross-section.